There is an issue with the default profile picture, it's 128x128 pixels but codeforces only lets you upload a profile picture with >=150 pixels. So, if you change your profile picture once and want to put the original profile picture back, it's impossible.

Please fix this MikeMirzayanov, if it's gonna be an issue to decrease the size limit from 150 pixels to 128 pixels, at least add an option to reset the profile pictures.